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x,y-nr reale pozitive
a)x³+y³≥x²y+xy²


Răspuns :

[tex] x^{3}+ y^{3}=(x+y)( x^{2} +xy+ y^{2}) [/tex]
[tex] x^{2} y+x y^{2}=xy(x+y) [/tex]
[tex](x+y)( x^{2} +xy+ y^{2}) \geq (x+y)( x^{2} + y^{2}) [/tex]
([tex] x^{2} +xy+ y^{2} \geq x^{2} + y^{2} [/tex]
[tex]xy \geq 0[/tex]
ceea ce trebuia de demonstrat